Solubility is defined as: the mass of a substance which will dissolve in 100g of water at a stated temperture.
A SOLUTION CONSISTS OF - solute & solvent.
Solute: This can be a solid, liquid or a gas. A solute dissolves in the solvent.
Solvent: The most common solvent is water but others include ethanol and trichloroethane.
(N.B) solution = solute + solvent.
A solution may be:
(1) CONCENTRATED : This has a high proportion of solute ( to remember, think about undiluted orange juice!!)
(2) DILUTE: This is the opposite of a concentrated solution. It
has a low proportion of solute.
Another fact which must be learnt is what the "concentration of a solution" is. * This is the amount of solute dissolved in a certain volume.* A "saturated solution" is one which contains as much solute as it can hold at that temperature. To allow more solute to dissolve in the solution at the some volume the temperature must be raised. However, gases are the opposite -
they are less soluble at higher temperatures.
A graph of solubility against temperature is called a solubility curve.
A material is soluble if it dissolves in a solvent.
A material is insoluble if it fails to dissolve in a solvent.
A substance is called slightly/sparingly soluble if it dissolves only in a little solvent.
(e.g) Ca (OH)2 is slightly soluble.
Mg (OH)2 is sparingly soluble.- In group one all the compounds of the elements are 'soluble'. This is because their compounds are ionic and divide up into separate ions.
- In group two many of the compounds are 'insoluble' (e.g) calcium carbonate (chalk and limestone.)
When carrying out a solubility experiment, it is important to remember that essentially 2 readings are needed to calculate the solubility. These are:
(1) Mass of the solution. (2) Mass of the solvent.Theses can be easily remembered in the equation:
Solute x 100 = Solubility.
Solvent
Mass of solute - g
Mass of solvent - gAfter dividing the mass of the solute by the mass of the solven it is necessary to multiply by 100 as solubility is the mass of substance dissolved in 100g of water at a stated temperature.
Remember that mass is found using a TOP PAN BALANCE.
The worked calculations below will help you to understand a question on solubility. (N.B) Often examiners also ask you a question which asks you to draw a solubility curve but DON'T
WORRY, points/readings for plotting the graph are usually given.(1) Example: Calculate the solubility of potassium chloride at 40 C, using the following results:
Mass of dish = 36.22g
Mass of dish and solution = 49.88g Mass of dish and solute = 39.88g(N.B) If carrying out a solubility practical record these 3 masses.
(a) Find the mass of the solution:
(Mass of dish & solution) - (Mass of dish). 49.88g - 36.22g = 13.66g.(b) Then find the mass of the solute:
(Mass of dish & solute) - (Mass of dish).39.88g - 36.22g = 3.66g
(c) Having found the mass of solution and solute, use them to find the mass of the solvent:
(Mass of solution) - (Mass of dish)
13.66g 3.66g = 10g.
(d) Now use the equation to calculate solubility:
Solute x 100 = solubility.
Solvent
3.66 x 100 = 36.6g/100g.
10(2) Example:
The solubility of sodium chloride at 20oC is 36.0g/100g of water, and at 100 C it is 39.8/100g of water.
a) How much sodium will dissolve in 200g of water at 20oC ?
b) If the solution in (a) is heated to 100oC, how much moresodium chloride will dissolve ?
Answer:
We know that solubility at 20oC is:
36.0g/100g = 20oC
? g/100g = 20oC
We notice that the mass of water has doubled so the mass of solute must be multiplied by 2 also:
36.0g/100g x 2 = 72.0g/200g.
Ans: 72.0g
(b) At 200oC 36.0g/100g.
At 200oC 39.8g/100g.
We are looking for the increase in solubility:
100oC 39.8g/100g.
200oC - 36.0g/100g. 03.8g/100g.However this answer is only /100g of solvent and we are asked for /200g of solvent so 0.38g must be multiplied by 2.
0.38g x 2 = 7.6g.Loreto College, Coleraine.